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UPSTREAM: doc: Document how to apply fdt overlays 

We have the capability to apply overlays on the command line but
we didn't have a document explaining how.

Change-Id: Idec1c3eac1ef3b52f4329d2ce9bffdd8b9aac32b
Signed-off-by: Pantelis Antoniou <pantelis.antoniou@konsulko.com>
Reviewed-by: Łukasz Majewski
Acked-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Kever Yang <kever.yang@rock-chips.com>
(cherry picked from commit d80162cfc559491dee3009b120e7268e9388302f)
This commit is contained in:
Pantelis Antoniou 2017-09-04 23:12:18 +03:00 committed by Kever Yang
parent a116ed4929
commit 994d9d06da
1 changed files with 37 additions and 0 deletions
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U-Boot FDT Overlay usage (without FIT images)
=============================================
FDT overlays are now available for use even without FIT images.
It is not as automagic as with FIT images though and require a few
manual steps.
1. Figure out where to place both the base device tree blob and the
overlay. Make sure you have enough space to grow the base tree without
overlapping anything.
=> setenv fdtaddr 0x87f00000
=> setenv fdtovaddr 0x87fc0000
2. Load the base blob and overlay blobs
=> load ${devtype} ${bootpart} ${fdtaddr} ${bootdir}/base.dtb
=> load ${devtype} ${bootpart} ${fdtovaddr} ${bootdir}/overlay.dtb
3. Set it as the working fdt tree.
=> fdtaddr $fdtaddr
4. Grow it enough so it can 'fit' all the applied overlays
=> fdt resize 8192
5. You are now ready to apply the overlay.
=> fdt apply $fdtovaddr
Please note that in case of an error, both the base and overlays are going
to be invalidated, so keep copies to avoid reloading.
Pantelis Antoniou
pantelis.antoniou@konsulko.com
11/7/2017